The specific aims of this study are (1) to determine, in a case-control pilot study, if patients with HIV who have been treated with protease inhibitors for at least six months have endothelial dysfunction, as measured by brachial artery ultrasound and changes in blood flow and arterial diameter in response to hyperemia and nitroglycerin, and (2) to determine if patients with HIV not treated with protease inhibitors, have endothelial dysfunction, as measured by the same technique.